Fuses are presently used to protect electrical circuitry from excessive current flow, and a current-carrying portion of the fuse will literally melt, or “blow,” when the current passing through the fuse rises too high. When a fuse blows, it opens the electrical circuit path it was in, and components relying on the current flowing through that path no longer receive the current. In some situations, the opening of that electrical circuit path might not be immediately apparent to an operator of the system, and damage can occur to components in the system. For example, a three-phase power supply system may supply power to a load, and if a fuse blows in one of the phases, some types of loads will, by the nature of their operation (e.g., and not necessarily by design), draw increased current from the other two phases. This increased current draw risks damaging components in the system.
Accordingly, it is desirable to be able to detect a blown fuse quickly, so that those components may be shut down to avoid damage. However, the traditional method of detecting a blown fuse—a visual inspection of the fuse itself—may not be quick enough to avoid that damage.
To help detect a blown fuse, some fuses include switches that are thrown when the fuse blows. That thrown switch may be coupled to a monitoring circuit, which may detect the thrown switch and alert an operator. Such switched fuses are helpful, but they are not always available. For example, in certain higher voltage applications, a three-phase line may operate at potentials that are thousands of volts above the ground of an external monitoring circuit. It may be difficult, if not impossible, to find a switched fuse with enough voltage isolation to allow it to be used for such higher voltage applications. There are also systems that detect blown fuses by monitoring the voltage across each fuse individually. However these systems may require the use of a large number of isolation devices (one per fuse) for three phase systems. When there are multiple three phase circuits involved, it can become expensive to monitor each fuse individually.
Accordingly, there remains a need to promptly detect a blown fuse.